Coil structure for heat exchanger



Sept. 3, 1957 H. w. ANGELERY con. STRUCTURE FOR HEAT EXCHANGER FiledJan. 12, 1954 2 Sheets-Sheet l llliih INVENTOR.

HENRY l l ANGELERV fi w y 'dlav HA5 HTTOPNEKS Sept. 3, 1957 H. w.ANGELERY con STRUCTURE FOR HEAT EXCHANGER Filed Jan. 12, 1954 2Sheets-Sheet 2 INVENTOR. HENRY M/. ANGEL/FRY HIS ATTORNEYS United StatesPatent p COIL STRUCTURE FOR HEAT EXCHANGER Henry W. Angelery, Englewood,N. 3.

Application January 12, 1954, Serial No. 493,610

Claims. (Cl. 257-229) This application is a continuation-in-part of myearlier copending application, Serial No. 159,695, filed May 3, 1950,now Patent No. 2,713,994, dated July 26, 1955, which in turn is acontinuation-in-part of my abandoned application, Serial No. 40,959,filed July 27, 1948.

The present invention relates to improvements in heat exchangersdesigned to effect a transfer of heat between two fluids, to a systemfor maintaining a mass of fluid at a predetermined temperature, and moreparticularly to improvements in controlling the rate of heat transferbetween two fluids when the flow of the subject fluid varies or becomesintermittent.

The term subject fluid as used herein, is applied to the fluid whosefinal temperature and, if desired, state is to be controlled. The termregnant fluid as used herein, is applied to the fluid used to controlthe temperature or state or both, of the subject fluid.

In order to promote a most thorough and complete understanding of theprinciples of this invention, the following description is directedprimarily to the application of the invention to the transfer of heatfrom steam to water, wherein steam is the regnant fluid and water is thesubject fluid. It is to be understood, however, that it is not intendedto limit the application of the invention solely to such use.

In conventional out of contact heat exchangers, the rate of flow andheat content of the regnant fluid and the effective heat transfer arearemain substantially constant although the heat requirements of thesubject fluid may vary considerably. The only variations in the amountof heat transferred to or from the subject fluid are, therefore, due tochanges in the mean temperature differential between the subject andregnant fluids. This is fairly satisfactory when the subject fluid iswithdrawn at a more or less constant rate. It is unsatisfactory,however, when the rate of withdrawal of the subject fluid variesappreciably or is intermittent.

Thus, for example, when conventional heat exchangers are used to heatwater with steam, difliculties arise due to the overheating of the waterwhen its rate of flow is reduced to a minimum or stopped completely.This is usually due to the simple fact that the amount of heat availablefrom the steam greatly exceeds the amount of heat required by the waterat small or zero rates of flow. When, on the other hand, the rate offlow of the water is increased to above average, the amount of heat thatcan be absorbed by a given volume of water is too small to raise itstemperature to the desired point for the simple reason that the amountof heat made available by the steam is not suflicient to satisfy theheat requirements of the water.

The present invention is applicable to a heat exchanger of the typedescribed in my aforementioned patent applications wherein the flow ofthe regnant fluid is controlled in such a way that it both anticipatesand satisfies the heat requirements of the subject fluid to the end thatthe final temperature of the subject fluid will remain substantiallyconstant at widely varying rates of flow.

2,805,048 Patented Sept. 3, 1957 In the preferred form of the heatexchanger the water or other subject fluid is introduced through atubular conduit into the lower end of a shell or tank containing anaspirator, and as the fluid is introduced into the lower end of theshell or tank through the aspirator, the aspirator creates a zone ofreduced pressure which circulates the subject fluid within the shellpast a thermostat to regulate the flow of regnant fluid into heatingcoils within the shell.

The heating coils within the shell are disposed at different levelstherein and the coils are connected in parallel relationship betweeninlet and outlet headers within the shell, and the connections betweenthe inlet header and the heating coils are at different levels in thesame order that the coils are arranged in the shell. The regnant fluidis introduced into the inlet header through a riser so that the regnantfluid is free to enter the uppermost bank of coils first and thensuccessive banks of coils at lower levels to permit the heat transferaction to take place within the shell in counter-flow fashion.

These and other features of the present invention will be more fullyunderstood from the detailed description which follows, and by referenceto the accompanying drawings wherein:

Fig. l is a sectionalized view in perspective, illustrating onepreferred embodiment of the apparatus of this invention;

Fig. 2 is a plan view in cross-section of a heat exchanger designed forrelatively large capacities; and

Fig. 3 is a cross-section view in elevation illustrating anotherpreferred embodiment of the apparatus of this invention.

The embodiment illustrated in Fig. 1 includes a shell 10 having a bottom11 and a top 12, inlet and outlet connections 22, 24, respectively, topermit the water or other subject fluid to be introduced into the shelland withdrawn from within the shell, a vertical conduit 27 connected atits upper end to the inlet connection 22, a circulating tube 30containing a temperature-responsive element 29, such as a thermostat, acylindrical member 26 encircling the conduit 27 and the circulating tube30, a vapor inlet riser 19a which leads the steam or other regnant fluidinto a vertical vapor feed header 19, a vapor or condensate returnheader 20, a condensate return port 17, a bank of concentric spiraltubular elements 14 to conduct the steam or other regnant fluid from theheader 19 to the vapor or condensate return header 20, and finally adrain port 21 in the base 11 of the shell.

The bank of tubular elements 14 consists of a plurality of units 31,each unit including two pairs of spiral coil members substantially asshown. The innermost spiral coil member 32 begins at a unit vapor feedheader 34 connected to the vapor feed header 19 and, after making fourturns in an upward direction, reverses its direction and becomes theoutermost spiral coil member 36. After again making four turns in adownward direction, spiral coil member 36 ends at a unit vapor orcondensate return header 37 connected to the vertical vapor orcondensate return header 20. The spiral coil member 39 next to theinnermost spiral coil member 32 begins at the unit vapor feed header 34,makes four turns upwardly adjacent the first spiral coil member 32 andthen reverses its direction to become the next to the outermost downwardspiral coil member 40 terminating in the unit vapor or condensate returnheader 37 adjacent the outermost spiral coil member 36.

The diameters of the loops described by each of the four coil membersshown in Fig. 1 are different, but the tubes forming them are preferablyof the same diameter. The sum of the coil diameters of spiral coilmembers 32 and 36 is equal to the sum of the coil diameters of cellmembers as and 40 with the result that the length of the path throughone pair of coils, connected in series as shown, is equal to that of theother pair. Inasmuch as the tube diameters and the number of turns ofeach coil member are the same, it follows that the pressure drop throughone pair of coils must be equal to that through 'the other. p

It is to be understood, of course,- that the unit 31 of spiral tubularelements 14 is representative only of a plurality of such units that areconnected in parallel between the vertical vapor feed header 19 and thevertical vapor or condensate return header 20. If the pressure drop ofthe vapor flowing through the pairs of spiral coil members and thedesign capacity of the heat exchanger permit, it is, of course, withinthe contemplation of this invention to use only one unit of one or morepairs of spiral coil members. 7

By the same token, it is within the contemplation of this invention tohave three, four or more pairs of spiral coil members in each of one ormore coil units, so long as the sums of the diameters of the coilmembers in the various pairs are equal.

It is also to be understood that while the members in the various coilunits are most advantageously arranged concentrically to utilize to amaximum the space available within the shell, the invention is notlimited to such an arrangement but is intended to include anyarrangement wherein the heat transfer elements are connected in paralleland oifer the same resistance to the flow of fluid.

The tubular member 26 is supported from the bottom 11 by a number offeet 41. The upper end of the tubular member 26 is open for the passagethereinto of the conduit 27 and a tube 42 enclosing the thermostat leads44, as well as fluid from the upper zone of the tank 10. A partition 46is provided in the lower portion of the tubular member 26 to form aclosed well for the fluid to be heated entering the tube at the openupper end and to support the circulating tube which encloses thethermostat 29 and the thermostat lead enclosing tube 42. The circulatingtube 30 is open at the top to receive fluid from the upper zone of thetank 10 and opens into an aspirating chamber 47 to permit circulation ofat least part of the fluid in the shell through the tube. The conduit27, after passing through the partition 46, terminates in a nozzle 48that is in line with a difiuser 49 in the otherwise closed end 50 of thetubular member 26, said difluser terminating above the level of thebottom In operation, when it is desired to utilize the heat exchangerfor heating a liquid to be heated with a vapor, the liquid enters theshell through the conduit 27 when ever liquid is withdrawn from theoutlet connection 24 and, by reason of its passage through theaspirator, consisting of the chamber 47, the nozzle 48, and the diffuser49, induces a circulation of at least part of the liquid in the shellthrough the circulating tube 30 and past the thermostat 29. The flow ofcold liquid through the conduit 27 withdraws heat from the liquid in thewell formed by the tubular member 26 and the partition 46. This, inturn, withdraws heat from and thereby lowers the temperature of theliquid flowing through the circulating tube 30. The thermostat 29thereupon. operates to control the rate of flow and pressure of vaporinto the vertical feed header 19.

The steam or other regnant fluid is introduced into the upper portion ofthe header 19 through the vertical riser 190 located within the header,and the steam is then permitted to flow toward the lower portion of theheader and thence into the unit feed headers 34. This arrangementinsures a flow of steam first to the uppermost coil of bank 14 of coils,and then progressively to the next lower coils in sequence to theirrelative vertical location on the header 19, i. e., a supply of steamflows to the uppermost coil first then to that immediate below it, thento the next coil directly below until finally a t 4 supply of steam isfed to the lowest coil connected to the header 19 by feed headers 34'.

This arrangement permits heat transfer to be conducted in counterflowinstead of parallel and/ or cross flow. By having counterflow heattransfer, the temperature of the water nearest thetemperature-responsive element 29 is immediately atfected, therebydecreasing the time lag of impulse to the temperature-responsive element29 with changes in load.

The details of the control unit are more fully explained in myabove-identified copending application. For the present it suflices tosay that if the temperature drop at the thermostat is slight, thepressure of the vapor admitted to the tubular elements will besuflicient to fill only a portion thereof with the vapor, with theresult that the eflfective area of the heating surface will be small.if, on the other hand, the temperature drop is appreciable and thereforereflects a high. heat demand, the pressure of the vapor admitted intothe header will be sulficient to overcome the pressure drop through thecoils with the result that the effective area of the heating surfacewill be increased to the maximum.

When the flow of liquid withdrawn from the heat exchanger ceases or isbrought to: a minimum, the flow of liquid through conduit 27 decreasescorrespondingly. This esults in a decrease in the amount of heatWithdrawn from the liquid trapped in the well and brings about a rise inthe temperature of the liquid in circulating tube 30 that surrounds thethermostat 29. The thermostat 29 thereupon operates to decrease thepressure of the vapor feed supplied to the header. This, in turn, asshown in the above-mentioned copending application, results in thecondensation of a portion of the vapor within the coils, and, due to theaction of check valves in the vapor supply and condensate return lines,operates to decrease the effective surface area of the tubular elementsthat is available for transfer of heat from the vapor to the liquid.

If no heated liquid is withdrawn for a period of time sufficient toresult in the cooling thereof due to radiation losses from the shell,the liquid will circulate due to thermal action through the circulatingtube 30 and any appreciable temperature drop will be sensed by thethermostat 29 and be reflected in a resumption or increase in flow ofvapor through the tubular elements 14.

The embodiment illustrated in Fig. 2 is intended to show how a heatexchanger constructed in accordance with the principle of this inventionmay have its capacity increased to any desired degree. Any one bank ofcoils 14 can be increased practically without limit but, in order toavoid too great a pressure drop in the fluid flowing therethrough, ithas been found to be desirable to utilize two or more sets of verticalheaders 19 and 20 for the feed and return of vapor and vapor condensate.In this event the top unit will be connected to one set of headers 19and 20, the next unit to the other set of headers, and so on. Each ofthe headers 19 contains a riser 19a for admitting the heat thereinto.Still more capacity may be obtained by utilizing two or more banks ofcoils 14. The modification illustrated in Fig. 2 shows how four banks ofcoils may be placed in a single heat exchanger, each bank having twosets of feed and return headers. In this event, his not necessary tohave a well and thermostat within each bank of coils. It is sufficientto have one such control means in only one of the coil banks and it ispreferred, as shown in the drawing, to position the control means,including a tubular member 26, conduit 27 and circulating tube 30,centrally among the various banks of coils. The essential details of thecontrol means are the same as described with reference to Fig. 1.

The operation of this modification is likewise essentially the same asthat of the embodiment illustrated in Fig. 1. If desired, the heatexchanger of this type may be provided with any suitable arrangement ofvertical and horizontal baflles to secure maximum contact of the fluidsin the shell with the surfaces of the reverse spiral coils.

"The embodiment illustrated in Fig. 3 is a modification ofthat'illustrated in Fig. 1 and is designed to reduce to an absoluteminimum the hunting of the temperature control system and to increase toa maximum the sensitivity of the thermostat to changes in thetemperature and/ or flow conditions of the subject fluid in the heatexchanger.

The heat exchanger illustrated in Fig. 3 includes a shell having abottom 11a and a top 120, a drain 21a, several banks of concentricspiral tubular elements 14, a vapor inlet riser 19:: leading into avapor feed header 19, a vapor or condensate return header 20 which leadsto an outlet port, liquid inlet and outlet connections 22 and 24 and athermostat 29. The bank of tubular elements 14 of Fig. 3 issubstantiallly identical with the bank of tubular elements14 illustratedin Fig. l of the drawing. The unit vapor feed headers 34 and'unitvapor'or condensate return headers (behind headers 34 in Fig. 3) arelikewise similar to those illustrated and described with reference toFig. 1.

An inlet conduit 52 is secured to the inlet connection 22 and isprovided with a constriction or nozzle 54 at a point spaced from itslower end 56. The thermostat leads 44 are enclosed in a cable or tube 42which is, in turn, enclosed in a circulating tube 57 that issubstantially parallel to the conduit 52. The upper end of the tube 57is spaced from the top 12a of the shell or suitably provided with one ormore openings 58 to permit the entry into the tube of at least a part ofthe liquid from within the shell. A support bracket 59 may be providedbetween conduit 52 and tube 57 to support the latter. A by-pass 60 isprovided between the conduit 52 and the tube 57, the connection of theby-pass with conduit 52 being upstream of the nozzle 54 and theconnection of the by-pass to the tube 57 being upstream of the locationof the thermostat 29 therein. It will be understood that additionalby-pass or sensing tubes may be connected to the tube 57, theseadditional tubes taking fluid from one or more points at lower levelsthan the by-pass 60. The lower end of the tube 57 communicates with theaspirating chamber and diffuser 61.

It will be apparent from this description that the thermostat 29 willsense immediately the introduction of fresh water due to the admixturethereof, at a point upstream from the thermostat, with the heated waterin the interior of the shell and in the upper portion of the tube 57, sothat the operation of the thermostat does not depend solely upon thewithdrawal of heat from the water in tube 57. Consequently, thethermostat 29, in eflfect, anticipates the heat transfer requirementswithin the shell 10 prior to an actual change in the temperature of thewater within the body of the shell.

When the discharge of water by way of the outlet connection 24 issuddenly stopped, the flow of fresh water through the by-pass 60 alsoceases immediately. If the water entering through inlet connection 22 iscolder than the water within the shell, as it will be when the heatexchanger is utilized as a water heater, and the movement of waterthrough the heat exchanger is stopped, the water surrounding thethermostat 2? quickly reaches the average temperature of the water inthe shell and is thus able to control effectively the further entry ofsteam into the tubular elements 14.

While the circulating means illustrated in Figs. 1-3 and described indetail herein are preferred as being the most simple in construction anddependable in performance, it is to be understood that it is within thecontemplation of the invention to place the thermostat and recirculatingtubes in a separate vessel connected with the shell for circulation ofthe water.

When the heat exchanger of the present invention is to be used as ahot-water heater, the water inlet 22 is connected to a suitable sourceof water, the water outlet 24 connected to the system to be heated, andthe riser 19a to a source of pre-heated fluid, such as steam. Thethermostat 29 will control a valve (not shown) in the steam line, sothat if the temperature sensed by the thermdstat'g'des below thepr-sele'cted temperature; thev valve? will be opened to admits'tea'm'to'the h'eader .19 and thence to: the tubular elements 14 undera pre-selected pressure until suflicient heat is absorbed by the liquidto raise the temperature to the ipre-s'elected 'value at which spirit ofthe invention. For example, although the heat exchanger of the presentinvention is described primarily.

as a hot-water heater, the heat exchanger-may be 'em-- ployed to cool orcondense vapor with'a liquid, or to. cool a fluid wit'hanother fluid orwith a vaporr These variations are described in the above-identifiedcopending application. It is to be understood, therefore, that thepresent invention is not to be limited to any specified form orembodiment, except insofar as such limitations are specified in theappended claims.

I claim:

1. A heating element for a heat exchanger comprising a tubular unit ofheat conductive material for conducting a fluid therethrough, saidtubular unit including four mutually concentric coils each having anumber of turns, the coils being telescoped, the innermost coil memberbeing connected in series to the outermost coil member by a firstreversely bent portion to form a first coil unit, and the twointermediate coil members likewise being connected in series by a secondreversely bent portion substantially concentric with and adjacent tosaid first reversely bent portion to form a second coil unit, said coilunits being of substantially equal length to provide two paths ofsubstantially equal length in parallel arrange ment between a source offluid and a discharge line.

2. A heat exchanger comprising a feed header, a return header, aplurality of banks of heating elements connecting the feed header andthe return header, each bank including four mutually concentric, helicalcoil elements, each coil element having a plurality of turns, theinnermost coil member having one end connected to one of said headersand its opposite end connected in series by a reversely bent portion toan end of the outermost coil member, the opposite end of the outermostcoil member being connected to the other header to form a first coilunit, the two intermediate coil members each having an end connected toa different header and their opposite ends connected in series by areversely bent portion to form a second coil unit, the arrangement beingsuch that fluid in the feed header is directed to the return headerthrough said banks of heating elements, the fluid in each unit beingtransmitted through two paths in parallel, each path being substantiallyequal in length and winding helically about the common axis first in onedirection and then reversing and winding about the common axis in theopposite direction, said headers supporting said coils in space with theends of said coils connected by said reversely bent portions free tomove relative to said manifolds to enable said coil units to expand andcontract relative to each other and to said manifolds.

3. A heating element for heat exchangers and the like comprising twocoil members of substantially equal length, one of said coil membershaving an inner substantially helical coil portion and an outersubstantially concentric, helical coil portion, said coil portions being'in spaced relation to provide a curved space therebetween,

said inner and outer coil portions being joined at one end by areversely bent portion, the other coil member having parallelsubstantially helical coil portions disposed in said space between saidinner and outer coil portions of said one coil member and being joinedat one end by another reversely bent portion, a supply manifold elementconnected to one end of each of said coil members to supply fluidthereto, and a return manifold element connected to the opposite end ofeach of said coil memhere to receive the fluidtherefrom, said manifoldelements supporting: said coilsfreely in space with the reversely' bentportions of said coil free to move relative- 4. A heating element forheat'exchangers comprisin a pair of heating coils formed of equallengths of tubular material; each cell including an inner helical coilportion wound inone direction andan outer helical coil portion wound inthe opposite direction, one cell having its coil portions adjacent toeach other and the other coil having its cell portions on' oppositesides of the coil stantially concentric', reversely bent portions insideby 15 side: relation.

U The heating element set forth in claim 4 comprising an inletmanifold-member connected to one end of each coil and a. dischargemanifold connected to the other end oieachicoil.

References Cited in the file of this patent UNITED STATES PATENTS916,936 Taylor Mar. 30, 1909 1,526,320 Cook Feb. 17, 1925 1,746,158Lofiler Feb. 4, 1930 1,825,433 White Sept. 29, 1931 1,961,202 De BaufreJune 5, 1934 2,249,074 Wolfert July 15, 1941 2,300,634 Schoenfeld Nov.3, 1942' 2,713,994v Angelery July 26, 1955-

